The present invention relates to a storage device control method, motor control method, and storage device, and more particularly to a storage device control method, motor control method, and storage device for changing a drive current waveform.
It is known that information recording/reproducing devices use various types of media such as optical disks and magnetic tapes. Among others, hard disk drives are widely used as a computer's storage device and recognized as being essential to the present-day computer systems. Owing to their excellent characteristics, the hard disk drives have found increasingly wide applications including computers, motion picture storage/reproducing devices, car navigation systems, and removable memories for use, for instance, in digital cameras.
A hard disk drive comprises a magnetic disk for storing data, a spindle motor for rotating the magnetic disk, a magnetic head for reading data stored on the magnetic disk and/or writing data onto the magnetic disk, and an actuator to which the magnetic head is fastened. The actuator is driven by a voice coil motor (VCM). The actuator pivotally moves on a pivot to move the magnetic head. To read/write data, the actuator moves the magnetic head to a data area on a rotating surface of the magnetic disk. The magnetic head has a recording/reproducing thin-film element and a slider. The pressure produced by the stiction of the air between the slider's ABS (Air Bearing Surface), which faces the magnetic disk, and the rotating magnetic disk properly balances with the pressure that the actuator applies toward the magnetic disk. As a result, the magnetic head flies above the magnetic disk with a fixed air gap.
The spindle motor is controlled for its driving by a CPU and a spindle motor driver (SPM driver). In compliance with a command from the CPU, the SPM driver provides control over spindle motor startup and rotation. When the actual rotational speed of the spindle motor is detected, feedback control is exercised to control the rotation of the spindle motor. While no data read/write process is performed during the use of a hard disk drive based on the load/unload technology, the magnetic head rests on a ramp mechanism positioned outside the magnetic disk. When a storage area on the magnetic disk needs to be accessed, the actuator turns to move the magnetic head from the ramp mechanism to a position above the magnetic disk. When the magnetic head moves to a position above the magnetic disk, air friction occurs between the magnetic head and magnetic disk. This air friction causes a change in the rotation of the magnetic disk.
A technology for controlling a change in the rotation of the magnetic disk, which may be caused by the above-mentioned loading operation, is disclosed by Japanese Patent Laid-open No. 2001-14789. When head load control is exercised in a load/unload type disk drive, the control gain of a feedback control system for the spindle motor is set to a high level. When the rotation reaches its steady state, the control gain is restored to the normal level. In the head loading sequence, the CPU increases the control gain to provide improved response to disturbance for the purpose of controlling a rotational change. When the controlled rotational change is within an acceptable range, the CPU restores the control gain to its normal level for the purpose of maintaining feedback control system stability.
In the magnetic head loading sequence, the control gain is increased to provide improved response to disturbance for the purpose of exercising rotational change control. When the control gain increases, feedback control system stability may decrease to incur oscillation. Therefore, when the controlled rotational change is within an acceptable range, the control gain is restored to its normal level. When the magnetic head is loaded onto the magnetic disk for data recording/reproducing purposes, the rotation of the spindle motor changes due to disturbance caused by the force of air friction between the magnetic head and magnetic disk. However, the use of the above configuration makes it possible to control such a change in the rotation of the spindle motor within a short period of time.